It is known that the intimate proximity of a diamond layer upon integrated circuits and any other high power density devices makes for unexcelled performance at high temperature as well as for convenience of cooling, to list a few desirable characteristics. It is also known that these desirable features of a diamond layer upon an integrated circuit are vastly improved when the layer is maintained at high uniformity, without irregularities. Depositing a diamond layer by chemical vapor deposition (CVD) is known to be one of the best methods for achieving a uniform diamond layer with high power density devices or other forms of integrated circuits. It is known to those familiar with the art that diamond CVD is typically performed by one of three major methods. Namely, 1) plasma enhanced diamond CVD (from DC, RF, or microwave energy sources); 2) hot-filament enhanced diamond CVD (primarily super hot tungsten wires as the source of energy); and 3) high velocity plasma torch diamond CVD. It is further known to those familiar with the art that all of the aforementioned processes result in the generation of significant heat from the plasma and/or highly heated wires, as well as, from highly significant exothermic recombination of atomic hydrogen on all surfaces closest to the plasma, or super hot wires.
The CVD process is carried out in an evacuated reaction chamber having a compound semiconductor substrate or a combination of semiconductor layers with other possible layers on some substrate placed therein, the top surface being covered with a diamond-friendly adhesion layer. “Diamond-friendly” means materials that have the potential to form binary or ternary chemical bonds with carbon. In essence the superior adhesion of diamond to these materials is not just a function of surface treatment and mechanical interlocking, but also of chemical bonding. Using CVD, the diamond layer is grown directly upon the diamond-friendly adhesion layer material which is preferably a dielectric such as silicon nitride, silicon carbide, aluminum nitride, or amorphous silicon, to name some examples. The carbon for growing the diamond layer is supplied by at least one carbon-bearing gas in a mixture with other reactive and possibly non-reactive (diluent) gases introduced into the reaction chamber for the CVD process. Almost always the carbon-bearing gas(es) are introduced into the process chamber in combination with hydrogen gas. Typically hydrogen comprises up to 90 to 99%, by volume of all gases supplied into the reaction chamber. Typical carbon-bearing gases used for such applications include CH4, C2H6, CO, and C2H2, with CH4 being the preferred gas for most such processes.
While CVD is the best known process for growing a diamond layer on the adhesion layer, there are aspects to CVD which require improvement for successful application of a diamond layer onto a compound semiconductor layer, and it is in these areas of improvement that this invention is directed. First, despite the benefits gained in growing diamond layers on standard compound semiconductor layers or compound semiconductor substrates through CVD, the underlying structures are not immune to plastic deformation (warpage). Warpage of any kind renders, at best, a substrate that will exhibit sub-par performance, and is therefore essentially useless. Warpage originates in the substrate due to nonuniform heating of the substrate when power directly or indirectly is ramped to the substrate either at too fast a rate or nonuniformly. So far the art has not obtained success at avoiding warpage on standard manufacturing-level compound semiconductor substrates (having a typical thickness range of 0.3 mm to 0.7 mm), during diamond layer growth through CVD. Some success has been achieved in avoiding warpage with non-standard semiconductor substrates, relating mainly to small parts in a research and development context, but never at a manufacturing level. These experimental parts typically have thicknesses of over two millimeters. Secondly, application of the carbon-bearing gas in too high of a concentration for a particular adhesion layer material will result in non-adhesion of the diamond layer due to high carbon soot formation at the deposition interface. Thirdly, application of carbon-bearing gas at too low of concentration could result in etching of the adhesion layer, resulting in direct but non-reproducible adhesion between the diamond and the compound semiconductor.
The foregoing reflects the state of the art of which the inventor is aware, and is tendered with a view toward discharging the inventor's acknowledged duty of candor, which may be pertinent to the patentability of the present invention. It is respectfully stipulated, however, that the foregoing discussion does not teach or render obvious, singly or when considered in combination, the inventor's claimed invention.